payloads/libpayload/libc/ipchecksum.c

   1 /*
   2  *
   3  * It has originally been taken from the FreeBSD project.
   4  *
   5  * Copyright (c) 2001 Charles Mott <cm@linktel.net>
   6  * Copyright (c) 2008 coresystems GmbH
   7  * All rights reserved.
   8  *
   9  * Redistribution and use in source and binary forms, with or without
  10  * modification, are permitted provided that the following conditions
  11  * are met:
  12  * 1. Redistributions of source code must retain the above copyright
  13  *    notice, this list of conditions and the following disclaimer.
  14  * 2. Redistributions in binary form must reproduce the above copyright
  15  *    notice, this list of conditions and the following disclaimer in the
  16  *    documentation and/or other materials provided with the distribution.
  17  *
  18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  28  * SUCH DAMAGE.
  29  */
  30
  31 #include <libpayload.h>
  32
  33 unsigned short ipchksum(const void *vptr, unsigned long nbytes)
  34 {
  35         int sum, oddbyte;
  36         const unsigned short *ptr = vptr;
  37
  38         sum = 0;
  39         while (nbytes > 1) {
  40                 sum += *ptr++;
  41                 nbytes -= 2;
  42         }
  43         if (nbytes == 1) {
  44                 oddbyte = 0;
  45                 ((u8 *) & oddbyte)[0] = *(u8 *) ptr;
  46                 ((u8 *) & oddbyte)[1] = 0;
  47                 sum += oddbyte;
  48         }
  49         sum = (sum >> 16) + (sum & 0xffff);
  50         sum += (sum >> 16);
  51         return (~sum);
  52 }